We were using the Olds mostly and the Nissan didn't get much use. So it was quite a while before I needed to fill the Nissan tank again.

When I did fill it, it leaked again! Twice I had tried to have the leak stopped and twice it had continued leaking.

After a lot of study and thinking, I determined that the first mechanic was wrong. Based on what the first mechanic told me, the second mechanic took my word for it that I needed a new fill tube. He did exactly what I ordered. He replaced the fill tube; but the tank continued to leak when full.

Notice on the diagram above: the fill tube is about half way down the tank. If it leaked from the fill tube, it would leak constantly until the fuel level was about half full.

Since my leak was only when the tank was full, it must be leaking at the top of the tank. So my attention shifted to the area around the fuel pump access. My first thought was that the old gasket caused the leak.

I asked the mechanic to inspect the pump gasket and replace whatever was causing the leak.

Guess what the problem was? One of the in-out tubes which enter the tank at the fuel pump access; it was old and cracked (sort of like me, ha ha).